Bronsted acid TfOH-mediated [3+2] cycloaddition reactions of diarylvinylidenecyclopropanes with nitriles

Diarylvinylidenecyclopropanes undergo a [3 + 2] cycloaddition reaction with MeCN in the presence of Bronsted acid TfOH to give the corresponding 3,4-dihydro-2H-pyn-ole derivatives 2 in moderate to excellent yields under reflux within a short time. As for the diarylvinylidenecyclopropane substrate containing a strongly electron-donating methoxy group on the benzene ring, the reaction leads to the formation of a different type of 3,4-dihydro-2H-pyrrole derivatives 4 under the same conditions.